The present invention relates to an adjustable implantation angle workpiece support assembly or structure coupled to an implantation chamber of an ion beam implanter and, more particularly, to a workpiece support assembly or structure that provides for rotational and linear movement of a workpiece with respect to an ion beam such that an implantation angle of the workpiece may be selected and the workpiece translated along a linear path at the selected implantation angle wherein a distance from an ion beam entrance to the implantation chamber to the intersection of the ion beam and an implantation surface of the workpiece remains constant during translation of the workpiece.
Ion beam implanters are widely used in the process of doping semiconductor wafers. An ion beam implanter generates an ion beam comprised of desired species of positively charged ions. The ion beam impinges upon an exposed surface of a workpiece such as a semiconductor wafer, a substrate or a flat panel, thereby xe2x80x9cdopingxe2x80x9d or implanting the workpiece surface with desired ions. Some ion implanters utilize serial implantation wherein a single, relatively large wafer workpiece is positioned on a support in an implantation chamber and implanted serially, that is, one workpiece is implanted at a time. The support is oriented such that the workpiece is in the ion beam beam line and the ion beam is repetitively scanned over the workpiece to implant a desired dosage of ions. When the implantation is complete, the workpiece is removed from the support and another workpiece is positioned on the support for implantation.
In recent years, the trend in the semiconductor industry has been to use increasingly larger wafer workpieces, for example, 300 mm. diameter wafers. The ability to implant large wafer workpieces or other workpieces such as flat panels has become very desirable. One way to implant a workpiece serially is to move it in front of a scanned, fanned or ribbon ion beam. Such an ion beam is wide enough so that the entire width of the workpiece can be implanted uniformly. In order to implant the entire workpiece, a second motion transverse to a direction or extent of the ion beam is required. Further, it is often desired to be able to change an angle of implantation for a particular workpiece being implanted. The angle of implantation is the angle of incidence formed between the ion beam and the treatment surface of the workpiece. An implantation angle of 0 degrees means that an implantation surface of the workpiece is normal to the ion beam beam line.
One shortcoming of workpiece support structures of prior art ion beam implanters is that, other than an implantation angle of 0 degrees, movement of the workpiece along a path of travel perpendicular to the ion beam beam line causes a distance that the beam travels within the implantation chamber before striking the workpiece implantation surface to change. Stated another way, if the implantation angle is not 0 degrees, the workpiece can be viewed as being tilted with respect to the ion beam beam line. If such a tilted workpiece is moved perpendicularly with respect to the ion beam beam line, when portions of the workpiece tilted toward the ion beam are being implanted, a distance that the ion beam travels in the implantation chamber before striking the implantation surface will be reduced compared to the beam distance at a center of the workpiece implantation surface. On the other hand, when portions of the workpiece tilted away from the ion beam are being implanted, a distance that the ion beam travels in the implantation chamber before striking the implantation surface will be greater compared to a beam distance at a center of the workpiece implantation surface.
Obviously, the larger the workpiece and the greater the implantation angle is from 0 degrees, the greater the difference in the beam distance traversed by the ion beam within the implantation chamber as implantation moves from one end of the workpiece implantation surface to an opposite end of the implantation surface. As the ion beam tends to diffuse over its beam path, non-constant beam distance may have an adverse effect on achieving a uniform ion dosage implantation over an entirety of the workpiece implantation surface. Thus, the trend toward larger wafers exacerbates this non-constant beam distance problem.
To insure uniform implantation of a workpiece implantation surface, it would be desirable to maintain a substantially constant beam distance traversed by ion beam within the implantation chamber before striking the implantation surface of the workpiece. What is desired is a workpiece support structure that provides the capability of selecting a desired implantation angle and then maintaining a substantially constant beam distance between entry of the ion beam into the implantation chamber and impacting the implantation surface while the workpiece is moved with respect to the ion beam beam line during the implantation procedure.
One exemplary embodiment of the present invention concerns an ion beam implanter having a workpiece support structure or assembly for supporting a workpiece within a vacuum or implantation chamber. The ion beam implanter includes an ion beam source for creating an ion beam and a beam line for transporting the ion beam along a path of travel and being scanned along an axis. A workpiece is supported by the workpiece support structure in the implantation chamber such that the workpiece is positioned to intersect the path of travel of the scanned ion beam for implantation of a implantation surface of the workpiece by the ion beam. Advantageously, the workpiece support structure provides for: a) selecting a desired implantation angle; and b) moving the workpiece for implantation of the implantation surface by the ion beam while maintaining a substantially constant beam distance between entry of the ion beam into the implantation chamber and striking the implantation surface.
The workpiece support structure is coupled to the implantation chamber and supports the workpiece. The workpiece support structure includes a first rotation member rotatably coupled to the implantation chamber, the rotation member having an axis of rotation perpendicular to a path of the ion beam and defining an opening through a width of the rotation member and offset from the rotation member""s axis of rotation. The workpiece support structure further includes a second rotation member rotatably coupled to the first rotation member and having an axis of rotation offset from the axis of rotation of the first rotation member. The second rotation member overlies and seals the opening in the first rotation member.
The workpiece support structure additionally includes a third member fixedly attached to the second rotation member. The third member including a rotatable drive having an axis of rotation aligned with the axis of rotation of the first rotation member and also aligned with an implantation surface of the workpiece to be implanted. A workpiece holder is attached to the rotatable drive of the third member and extends through the first and second rotation members into the implantation chamber and supports the workpiece within the implantation chamber. Rotation of the first rotation member and the third member rotatable drive changes an implantation angle of the workpiece with respect to the path of the ion beam in the implantation chamber. Proper rotation of the first rotation member, the second rotation member and the third member rotatable drive results in a linear movement of the workpiece along a path of travel in a direction transverse to the ion beam while maintaining the a selected implantation angle.
Advantageously, a distance between entry of the ion beam into the implantation chamber and an intersection of the ion beam and a surface of the workpiece remains substantially constant during movement of the workpiece along its linear path of travel.
These and other objects, advantages, and features of the exemplary embodiment of the invention are described in detail in conjunction with the accompanying drawings.